Dynamics of rod-like macromolecules in concentrated solution. Part 1

Abstract

A concentrated solution of rod-like macromolecules is thermodynamically ideal if the rods are thin enough, but its dynamical behaviour is completely different from that of a dilute solution because of the “entanglement” constraint that the rods cannot pass through each other. This characteristic feature is discussed. First the basic kinetic equation which describes the Brownian motion is set up. This equation is then applied to two particular experiments, the Kerr effect and dynamic light scattering. The principal results are : (1) The characteristic relaxation time τ_r of the Kerr effect is very long, and depends strongly on the concentration ρ and the molecular weight M such that τ_r∝ρ²M⁷, and the relaxation is non-exponential. (2) The dynamical structure factor S(k, t) measured by light scattering has a characteristic shape which is independent of concentration; the initial slope of S(k, t) being about half the value predicted for dilute solution; S(k, t) has a very long tail as S(k, t)∝ 1/√t.